var a = '[a, b, c, d]'; var b = [1, 2, 3, 4];
if (Array.isArray(a)){
    document.write("a是数组");
}else {
    document.write("a不是数组");
}
if (Array.isArray(b)){
    document.write("b是数组");
}else {
    document.write("b不是数组");
}